That's a very interesting question you've asked. Here's my take on it.

I think the answer is "it depends". At the beginning of your programming career, coding skill is essential, because if you have no skill, then you can't produce. As your coding skills increase, so does your productivity.

Switching emphasis to productivity occurs once coding skills reach a level where, as you said, increased skill doesn't translate into increased productivity. And I think the real trick is determining what that level is. It's a combination of goal (for a given problem, how much skill is required, and when must the solution be available) and cost of improving your skills.

I partially disagree that coding skill is simply a means to an end. Some people aren't programmers by trade. They do so for the pure pleasure of coding, in which case productivity isn't part of the equation. For the purpose of this discussion, I'm talking about professional programming, in which case you're absolutely right.

Phemur